The present invention relates to a method of inspecting the pattern on a photographic mask used in the manufacture of semiconductor devices, and more particularly the invention relates to a method of inspecting for the presence of defects in a photographic mask such as foreign particles, e.g., dust deposited on the surface of the mask and flaws caused in the mask surface during the mask cleaning process and the like.
In the recent manufacturing procedures of LSIs and VLSIs, the photoengraving process has been made increasingly precise and the tendency of circuit patterns has been toward further reduction in linewidth. Paralleling this, there has been a proportionate increase in the occurrence of a situation in which foreign particles, e.g., dust suspended or generated in the production environment deposits on a photographic mask or a reticle and causes defects in semiconductor devices.
Recently, exposure apparatus of the type repeatedly projecting a reduced image of a pattern onto a plurality of areas on a semiconductor wafer has been watched and used widely. If a photographic mask or a reticle contaminated with such foreign particles is used as a master plate for the pattern projection in this type of exposure apparatus, defects will be caused in all of the exposed areas and the yield of produced semiconductor devices will be decreased. Thus, it is essential to exactly inspect preliminarily for the presence of foreign particles on a mask or a reticle.
Methods heretofore known for inspecting the pattern of a mask or reticle include one in which the pattern of a mask or reticle is printed on a wafer and the wafer is inspected with the naked eye through an optical microscope. While this method effects the defect inspection of the pattern on a mask or reticle with the mask or reticle being mounted in place in the exposure apparatus, thereby performing the inspection which meets the production environment, there is a disadvantage in that the method requires much time and is low in reliability due to the macroscopic inspection with the use of an optical microscope. Another known method inspects a mask or a reticle itself and this method is still insufficient for producing defect-free semiconductor devices in that there is the danger of dust or the like depositing on the inspected mask at the stage of mounting it in the exposure apparatus.